1. Field of the Invention
The present invention relates to a nanofiber, especially to a nanofiber and a photovoltaic device comprising patterned nanofiber.
2. Description of the Related Art
Large-area solution processible organic photovoltaic (OPV) have attracted extensive scientific interest for renewable energy conversion due to the advantages of inexpensive, low fabrication temperature, and mechanical flexibility. Currently, the power conversion efficiency (PCE) of polymer-fullerene bulk-heterojunction OPVs over 9-10% are reported for single junction devices as well as tandem solar cells. However, with the comparatively low charge carrier mobility (usually less than 10−4 cm2V−1s−1) of photo-active polymers, the quantum efficiency of OPV is relatively limited. Thus, it is common to use a thinner polymer film for preventing the exciton recombination, leading to higher internal quantum efficiency. The minimized photo-active layer, however, is required to harvest sufficient incident photons. Therefore, it remains a challenge using thin polymer films to create a more efficient light trapping and coupling environment for high performance OPV devices.
Light trapping method based on the surface plasmon resonance (SPR) effect was widely used to enhance OPV device performance recently. Metallic nanostructures such as Au, Ag, or Al were employed to improve OPV PCE in a range of 10-25% via the enhancement of localized surface plasmon resonance (LSPR) near field absorption. Also, several studies have reported that the LSPR from the metallic clusters would exhibit stronger local electrical field as compared to isolated particles due to the collective SPR with inter-particle plasmon coupling. In addition, Au—Ag alloy or silica-coated noble metal nanoparticles used in the photo-active layer resulted in a 14-30% improvement in PCE very recently. Especially, a silica shell layer of the metal/SiO2 core/shell nanoparticles was enabled to act as an electrically insulating interface, which would not interfere with exciton generation and transport into the photo-active polymer layer. To further improve the electrical conductivity, besides, metallic nanoparticle assemblies formed supplemental charge transportation networks.
Electrospinning (ES) is a high-throughput processing technique to fabricate micro- or nanofibers from polymer solutions. The non-woven or well-aligned nanofibers prepared from semiconducting materials could be produced by the ES technique, and used for optoelectronic device (field-effect transistor, OPV, and memory) applications. The plasmonic nanoparticle-incorporated electrospun fibers enable unique one-dimensional metallic nanoparticle assemblies, which can introduce into the OPV system for light trapping. There has reported that Au and Ag nanoparticles were co-spun with polyethylene and poly(vinyl alcohol), respectively, with the encapsulated aggregates of plasmonic nanostructures. Indeed, Au nanorods were incorporated into poly(acryl amide) uniaxially-aligned ES fibers for waveguiding applications with photon-to-plasmon conversion efficiency of 70%. However, the applications of such nanofibers in bulk-heterojunction OPV devices have not been explored yet, as far as we know. In addition, the effect of the fiber architecture on the OPV performance is also not investigated.